You don't need a cheap travel insurance, you will need one which is covering your diabetes completely. Normally diabetes is a pre-existing condition and not covered by most insurances except explicitly agreed on in written form. You have to ask in any case before you sign something.
We've just done ours,ive got diabetes 2,high blood pressure treatment,high cholesterol. My partner has had a dvt. We got joint cover,European inc cruising for £130 for year. We thought that was a GD deal. We got ours thro saga. Must b an age thing lol